Halo 3 Global Heatmaps

"Heatmaps are the Doppler Radar System of Death in Halo 3. We’re tracking encounters, weapons used and their results in a given game, collecting that data and sharing it with players visually. The key here is “the darker the red, the more frequent the deaths (or kills, depending on the parameters)."

Bungie Online: Halo 3 Global Heatmaps